An unknown killer preying on pigs in China has been identified as a new kind of coronavirus. And like the deadly SARS virus, this one also got its start in bats.

In late 2016, pigs mysteriously started having intense diarrhea and vomiting on farms in China’s southeastern Guangdong province. By May 2017, the disease had killed 24,693 piglets. Tests failed to pin the outbreak, which has since waned, on common pig viruses.

By analyzing samples from sick piglets, researchers pieced together the genetic blueprint of the virus causing swine acute diarrhea syndrome, or SADS. It shares 95 percent of its genetic code with another coronavirus, HKU2, detected in horseshoe bats in 2007. Evidence suggests these two coronaviruses share a common ancestor and that SADS jumped from bats to pigs, researchers report April 4 in Nature.

No farm workers tested positive for SADS, so the disease doesn’t appear to infect humans. But the first documented human cases of SARS, or severe acute respiratory syndrome, emerged 100 kilometers from the pig farms hit by SADS. The study adds to evidence that keeping an eye on bat viruses could reduce future viral outbreaks — in pigs and humans.

So sad

To figure out if the SADS virus isolated from sick piglets had been the cause of their demise, researchers infected healthy farm piglets with the virus. Three out of six died. Compared with intestinal tissue from healthy piglets (left), samples from sick ones showed signs of SADS virus proteins (red, right).

Editor’s note: This story was updated on April 20, 2018, to correct the year that HKU2 was detected in bats.